Mps-1 (Monopolar Spindle 1) kinase (also known as Tyrosine Threonine Kinase, TTK) is a dual specificity Ser/Thr kinase which plays a key role in the activation of the mitotic checkpoint (also known as spindle checkpoint, spindle assembly checkpoint) thereby ensuring proper chromosome segregation during mitosis [Abrieu A et al., Cell, 2001, 106, 83-93]. Every dividing cell has to ensure equal separation of the replicated chromosomes into the two daughter cells. Upon entry into mitosis, chromosomes are attached at their kinetochores to the microtubules of the spindle apparatus. The mitotic checkpoint is a surveillance mechanism that is active as long as unattached kinetochores are present and prevents mitotic cells from entering anaphase and thereby completing cell division with unattached chromosomes [Suijkerbuijk S J and Kops G J, Biochemica et Biophysica Acta, 2008, 1786, 24-31; Musacchio A and Salmon E D, Nat Rev Mol Cell Biol., 2007, 8, 379-93]. Once all kinetochores are attached in a correct amphitelic, i.e. bipolar, fashion with the mitotic spindle, the checkpoint is satisfied and the cell enters anaphase and proceeds through mitosis. The mitotic checkpoint consists of a complex network of a number of essential proteins, including members of the MAD (mitotic arrest deficient, MAD 1-3) and Bub (Budding uninhibited by benzimidazole, Bub 1-3) families, the motor protein CENP-E, Mps-1 kinase as well as other components, many of these being over-expressed in proliferating cells (e.g. cancer cells) and tissues [Yuan B et al., Clinical Cancer Research, 2006, 12, 405-10]. The essential role of Mps-1 kinase activity in mitotic checkpoint signalling has been shown by shRNA-silencing, chemical genetics as well as chemical inhibitors of Mps-1 kinase [Jelluma N et al., PLos ONE, 2008, 3, e2415; Jones M H et al., Current Biology, 2005, 15, 160-65; Dorer R K et al., Current Biology, 2005, 15, 1070-76; Schmidt M et al., EMBO Reports, 2005, 6, 866-72].
There is ample evidence linking reduced but incomplete mitotic checkpoint function with aneuploidy and tumorigenesis [Weaver B A and Cleveland D W, Cancer Research, 2007, 67, 10103-5; King R W, Biochimica et Biophysica Acta, 2008, 1786, 4-14]. In contrast, complete inhibition of the mitotic checkpoint has been recognised to result in severe chromosome missegregation and induction of apoptosis in tumour cells [Kops G J et al., Nature Reviews Cancer, 2005, 5, 773-85; Schmidt M and Medema R H, Cell Cycle, 2006, 5, 159-63; Schmidt M and Bastians H, Drug Resistance Updates, 2007, 10, 162-81].
Therefore, mitotic checkpoint abrogation through pharmacological inhibition of Mps-1 kinase or other components of the mitotic checkpoint represents a new approach for the treatment of proliferative disorders including solid tumours such as carcinomas and sarcomas and leukaemias and lymphoid malignancies or other disorders associated with uncontrolled cellular proliferation.
Different compounds have been disclosed in prior art which show an inhibitory effect on Mps-1 kinase: WO 2009/024824 A1 discloses 2-Anilinopurin-8-ones as inhibitors of Mps-1 for the treatment of proliferate disorders. WO 2010/124826 A1 discloses substituted imidazoquinoxaline compounds as inhibitors of Mps-1 kinase. WO 2011/026579 A1 discloses substituted aminoquinoxalines as Mps-1 inhibitors. WO 2011/064328 A1, WO 2011/063907 A1, WO 2011/063908 A1, and WO 2012/143329 A1 relate to [1,2,4]-triazolo-[1,5-α]-pyridines and their use for inhibition of Mps-1 kinase.
The above mentioned patent applications which are related to [1,2,4]-triazolo-[1,5-α]-pyridines mainly focus on the effectiveness of the compounds in inhibiting Mps-1 kinase, expressed by the half maximal inhibitory concentration (IC50) of the compounds. For example, in WO 2011/063908 A1 the effectiveness in inhibiting Mps-1 kinase was measured in an Mps-1 kinase assay with a concentration of 10 μM adenosine triphosphate (ATP). The cellular concentration of ATP in mammals is in the millimolar range. Therefore it is important that a drug substance is also effective in inhibiting Mps-1 kinase in a kinase assay with a concentration of ATP in the millimolar range, e.g. 2 mM ATP, in order to potentially achieve an antiproliferative effect in a cellular assay.
In addition, as one of ordinary skill in the art knows, there a many more factors determining the druglikeness of a compound. The objective of a pre-clinical development is to assess e.g. safety, toxicity, pharmacokinetics and metabolism parameters prior to human clinical trials. One important factor for assessing the druglikeness of a compound is the metabolic stability. The metabolic stability of a compound can be determined e.g. by incubating the compound with a suspension of liver microsomes from e.g. a rat, a dog and/or a human (for details see experimental section).
Another important factor for assessing the druglikeness of a compound for the treatment of cancer is the inhibition of cell proliferation which can be determined e.g. in a HeLa cell proliferation assay (for details see experimental section).
The successful delivery of a pharmaceutical to a patient is of critical importance in the treatment of disorders as well. The use of many clinical drugs with known bioactive properties is limited by the drugs' very low water solubility, making for example intravenous administration of the active ingredient difficult.
Intravenous (i.v.) medication administration refers to the process of giving medication directly into a patient's vein. Methods of administering i.v. medication may include giving the medication by rapid injection (push) into the vein using a syringe, giving the medication intermittently over a specific amount of time using an i.v. secondary line, or giving the medication continuously mixed in the main i.v. solution.
The primary purpose of giving i.v. medications is to initiate a rapid systemic response to medication. It is one of the fastest ways to deliver medication. The drug is immediately available to the body. It is easier to control the actual amount of drug delivered to the body by using the i.v. method and it is also easier to maintain drug levels in the blood for therapeutic response.
As a result of low water solubility, many drugs often are formulated in co-solvent pharmaceutical vehicles or as prodrugs.
A prodrug is an active drug chemically transformed into a derivative which by virtue of chemical or enzymatic attack is converted to the parent drug within the body before or after reaching the site of action. The process of converting an active drug into inactive form is called drug latentiation. Prodrugs can be carrier-linked-prodrugs and bioprecursors. The carrier-linked prodrug results from a temporary linkage of the active molecule with a transport moiety. Such prodrugs are less active or inactive compared to the parent active drug. The transport moiety will be chosen for its non-toxicity and its ability to ensure the release of the active principle with efficient kinetics. Whereas the bioprecursors result from a molecular modification of the active principle itself by generation of a new molecule that is capable of being a substrate to the metabolizing enzymes releasing the active principle as a metabolite.
Prodrugs are prepared to alter the drug pharmacokinetics, improve stability and solubility, decrease toxicity, increase specificity, and/or increase duration of the pharmacological effect of the drug. By altering pharmacokinetics the drug bioavailability is increased by increasing absorption, distribution, biotransformation, and/or excretion of the drug.
In designing the prodrugs, it is important to consider the following factors: a) the linkage between the carrier and the drug is usually a covalent bond, b) the prodrug is inactive or less active than the active principle, c) the prodrug synthesis should not be expensive, d) the prodrug has to be reversible or bioreversible derivative of the drug, and e) the carrier moiety must be non-toxic and inactive when released.
Prodrugs are usually prepared by: a) formation of ester, hemiesters, carbonate esters, nitrate esters, amides, hydroxamic acids, carbamates, imines, mannich bases, and enamines of the active drug, b) functionalizing the drug with azo, glycoside, peptide, and ether functional groups, c) use of polymers, salts, complexes, phosphoramides, acetals, hemiacetals, and ketal forms of the drug (for example, see Andrejus Korolkovas's, “Essentials of Medicinal Chemistry”, pp. 97-118).
It was therefore an object of the present invention to identify an Mps-1 kinase inhibiting compound or a prodrug derivative thereof which is characterized by a high druglikeness and which can be administered intravenously.